This invention relates to silver halide photographic materials, more particularly to a technique for reducing the increase in fogging and the resultant deterioration in granularity during prolonged storage of high-sensitivity photographic materials.
The recent advances in various sensitizing techniques have been remarkable and ultrahigh-sensitivity color photographic materials having speeds of 1000 and above in ISO designation are commercially available today. Heat- or moisture-initiated fogging during prolonged storage has been a well known problem with high-sensitivity photographic materials but the advent of more sensitive products has highlighted new problems that should by no means be neglected and they are the increase in fogging due to the effects of so-called "natural radiations" (i.e., environmental radiation and cosmic rays) and the resulting deterioration in granularity.
It has been reported that the fogging due to prolonged storage of high-sensitivity silver halide photographic materials and the resultant deterioration in granularity depend upon the inherent sensitivity of silver halide grains, the contents of silver and gold in photographic materials and the amount of potassium ions. Under these circumstances, the present inventors noted gold sensitizers as one of the factors to aging deterioration during prolonged storage of high-sensitivity photographic materials. Inorganic gold complex salts have been commonly used as gold sensitizers (see, for example, U.S. Pat. No. 2,399,083). Among the inorganic gold complex salts, chloroauric acid, potassium chloroaurate, potassium aurithiocynate and auric trichloride are currently used as advantageous gold sensitizers. However, these gold complex salts are prone to liberate gold and part of the liberated gold will form a stronger complex with gelatin and remain in the latter thereafter. Hence, deterioration in the performance of photographic materials that results from the use of gold sensitizers can be dealt with as a problem associated with the chemical properties of the gold sensitizers.